Project Summary/Abstract It is now widely recognized that the cerebellum (CRB) has widespread involvement in cognitive function and that cerebellar neuropathology is linked to cognitive disorders. Cerebellar involvement in cognitive functions occurs via neural circuits that connect the CRB and association areas of the cerebral cortex (CC). Currently, it is not known how neuronal activity exchanged via these circuits relates to cognitive function and whether deficits in cerebro-cerebellar (CC-CRB) interaction are causally involved in cognitive disorders. Dr. Heck?s lab recently developed an approach to investigate the neuronal mechanisms underlying cerebellar involvement in spatial working memory (SWM) as a cognitive function that is known to involve CC and CRB areas and is readily tractable in rodents. The medial prefrontal cortex (mPFC) and the dorsal hippocampal CA1 region (dCA1) are both essential for SWM and show increased coherence of local field potential (LFP) oscillations during SWM decision making. Preliminary studies in the Heck lab show that stimulating Purkinje cells (PCs) in CRB lobulus simplex (LS) causes an increase in LFP coherence between mPFC and dCA1 and improves SWM. PCs project to the excitatory cerebellar nuclei (eCN) neurons ? which integrate inputs from PCs, mossy and climbing fiber collaterals, and inhibitory interneurons ? so these neurons must be the next step for investigation. In addition, research by Dr. Joyner and others has shown that the Engrailed (En) genes are essential for developmental patterning of the CRB and mutations in the human EN2 have been implicated in cognitive disorders such as ASD. The Atoh1-En1/2 CKO mouse line developed by Dr. Joyner exhibits conditional loss of function of En1/2 in cerebellar excitatory neurons (eCN and granule cells) and, unlike models with global loss of En function, cerebellar cytoarchitecture is largely normal, only exhibiting a proportional scaling down of neuron number. We hypothesize that eCN activity is causally involved in controlling mPFC-dCA1 coherence and SWM decision making and that conditional loss of En1/2 expression will disrupt eCN control of mPFC-dCA1 coherence and SWM performance. Experiments outlined in this proposal will use multi-site extracellular recording, behavioral monitoring, and advanced optogenetics to: 1) investigate the role of eCN neurons in the modulation of mPFC- dCA1 coherence and SWM decision making in healthy mice in Specific Aim 1, 2) evaluate how loss of En1/2 expression in cerebellar excitatory neurons affects CC-CRB communication and cognitive function in Specific Aim 2, and 3) use optogenetic techniques to selectively manipulate eCN neuron activity in freely moving mice to determine whether eCN output is causally linked to mPFC-dCA1 coherence and SWM decision making in Specific Aim 3. Sponsors Drs. Heck, Joyner, and Chizhikov provide all the combined expertise necessary for excellent training and execution of the proposed experiments. If confirmed, results from this project would suggest that CC-CRB interaction and cerebellar coordination of movement both involve precise, cerebellar temporal coordination of events.